Speech enhancement systems in a motor vehicle must of course contend with low signal-to-noise ratio (SNR) conditions, but they must also contend with different kinds of noise, some of which is considered to be transient or “non-stationary.” As used herein, non-stationary vehicle noise includes but is not limited to, transient noises due to vehicle acceleration, traffic noises, road bumps, and wind noise.
Those of ordinary skill in the art know that conventional prior art speech enhancement methods are “retrospective:” they rely on detection and analysis of noise signals that have already occurred in order to suppress noise that is present or expected to occur in the future, i.e., noise that has yet to happen. Prior art noise suppression methods thus assume that noise is stable or “stationary” or at least pseudo-stationary, i.e. the noise power spectrum density (PSD) is stable and therefore closely approximated or estimated via a slow temporal smoothing over the noise detected.
When a background noise occurs suddenly and unexpectedly, as happens when a vehicle strikes a road surface imperfection for example, conventional prior art noise detection/estimation methods are unable to quickly differentiate noise from speech but require instead, significant amounts of future samples that are yet to happen. Traditional speech enhancement techniques are therefore inherently inadequate to suppress so-called non-stationary noises. A method and apparatus for detecting and suppressing such noise would be an improvement over the prior art.